This manner of procedure in the sheathing of a cable and the final vulcanization or polymerization of the insulating layer of the cable is known through DE-PS 27 26 767 in which the cable during the vulcanization or polymerization process respectively, is rotated about its longitudinal axis by a rotating device which grips the cable sheath. However the rotation is absorbed in a pulling mechanism directly before entrance of the cable into the extruder and does not proceed further.
It is an object of the apparatus of the present invention to prevent the fanning out of the twisted cable during the vulcanization or the polymerization process. Such fanning out would loosen the individual insulated conductors of the cable and the extrusion mass applied as the sheath could enter the interior of the cable and alter the desired cable dimension. Through the applied rotation, this unwinding of the twisted cable is prevented, whereby the twisting applied to the cable only in the region between the rotating device and the pulling device arranged just before the extruder can be developed, whereby the effective twisting produced in the cable by the passage of the cable through the polymerizing tube will be shifted along the axis of the cable, so that neither behind the rotating device in the winding up of the sheathed cable, nor before entry of the twisted, not yet sheathed, cable into the first pulling device, is any untwisting observable. By passage of the cable through the apparatus, the twisting of the cable produced by the rotary movement is shifted along the cable, so that the cable leaves the apparatus rotating device with approximately the same degree of twisting with which the cable entered the apparatus.
This process is, above all, useable where the sheathing to be applied is only a thin layer. With a thin sheathing it is most essential that the least possible sheathing material is pressed into the interior of the cable. If a thicker sheathing is to be applied to an electrical conductor or a conductor bundle, it is necessary to take care that gravity does not deform the still fluid cable sheath after the extrusion, before it is vulcanized or polymerized. Through DE-OS 19 33 043 it is known to compensate the force of gravity on the applied cable sheath by setting the entire apparatus together with the unwinding station of the unsheathed cable and the winding up station of the sheathed cable in rotation about the axis of the cable. This leads to a uniformly sheathed cable, but involves considerable expense and precludes continuous operation, because only the supply of unsheathed cable on a cable drum can be sheathed before the apparatus must be stopped, so that the cable drum can be replaced by a new one.
In the production of a thick walled sheathed cable, the apparatus of DE-PS 27 26 767 cannot be used because the rotary movement serves merely to tighten the twisting of the insulated conductors is not sufficient to prevent deformation of the cable sheath by gravity, while use of the apparatus according to DE-OS 19 33 043 is prohibited on account of the mass to be rotated and the impossibility of continuous operation.